Identification of Therapeutic Wavelengths For Photobiomodulation of Dental Pulp Cells

Methods: Human dental pulp cell (DPC) populations from 4 donors were isolated via an explant procedure and cultured in phenol-red-free α-MEM/10% FCS (Gibco, UK) at 37˚C in a humidified atmosphere containing 5% CO₂. DPCs at passages 2-4 were seeded (150µL; 25,000 cell/ml) in black 96-microwell plates with transparent bases (Corning, Sigma-Aldrich, UK). A total of 66 centrally located wells were seeded per plate (6 non-irradiated controls and 60 irradiated cultures). After 24h cultures were irradiated from directly below using a bespoke LED matrix containing 60 x 5mm epoxy encased LEDs (λ: 600nm-850nm; 10 rows, n=6) for time intervals of 30, 45 and 60s. Metabolic and mitochondrial activity was assessed via a modified MTT assay 4h following irradiation. Statistical differences were identified by using analysis of variance and post-hoc Tukey tests (P=0.05) and compared with non-irradiated controls.

Results: DPC metabolic/mitochondrial activity was dependent upon the exposure time and the LED wavelength applied. The wavelengths that gave significantly higher MTT absorbance (P<0.05) were 650nm, 660nm and 810nm. Within these wavelengths, significantly higher MTT absorbance was recorded for 30s and 45s exposure times (P<0.05).

Conclusion: Data indicated that therapeutic windows exist in terms of wavelength (650nm, 660nm and 810nm) and exposure time (<45s) for the photobiomodulation of DPCs. Clinically, LLLT of the dental pulp may minimise pain and accelerate tissue repair following trauma and restorative dental techniques.